1. Field of the Invention
The present invention relates to a dielectric ceramic composition used as, for example, a dielectric layer of a multilayer ceramic capacitor and the like, and an electronic component using this dielectric ceramic composition as a dielectric layer.
2. Description of the Related Art
A multilayer ceramic capacitor as one example of an electronic component is produced, for example, by alternately stacking a ceramic green sheet composed of a predetermined ceramic composition and an internal electrode layer having predetermined pattern, and cofiring a green chip thus obtained as one body. Since the internal electrode layer of the multilayer ceramic capacitor is formed to be one body with a ceramic dielectric body by firing, it is necessary to select a material which does not react with the ceramic dielectric body. Therefore, as a material to compose the internal electrode layer, conventionally, it has been forced to use expensive rare metal such as platinum, palladium and the like.
However, in recent years, since the dielectric ceramic composition using inexpensive base metals such as nickel, copper and the like has been developed, and significant cost down has been realized.
In recent years, demands for downsizing the electronic components along with the densification of electronic circuits, downsizing and making a larger capacity of the multilayer ceramic capacitor have been progressed rapidly. Along with that, each layer of the dielectric layer of the multilayer ceramic capacitor has become thinner, thus there are demands for the dielectric ceramic composition which can maintain the reliability as a capacitor even when it is made thinner. Particularly, for downsizing and making larger capacity of a mid-voltage capacitor used under high rated voltage, a great reliability is required for the dielectric ceramic composition.
Also, the multilayer ceramic capacitor using the dielectric ceramic composition including barium titanate as a main component showing ferroelectricity is accompanied with an electrostriction which generates a mechanical strain when electrical field is applied. In some cases a vibration noise generated by this electrostriction is in an uncomfortable range for human, thus a countermeasure is required.
Conventionally, as a technology in which the base metal can be used as a material to compose the internal electrode, and temperature change of capacitance is satisfying X7R property (within, −55 to 125° C., ΔC=±15%) of EIA standard, the present applicant has suggested the dielectric ceramic composition disclosed in JP Patent No. 3091192 and the like. However, since capacitance-temperature characteristic is important in this technology, a rare earth element having relatively small ion radius is added more than a rare earth element having large ion radius. Thus, it was insufficient to obtain the high reliability along with the downsizing and larger capacity of the mid-voltage capacitor. Further, there was a problem of electrostriction involved due to large specific dielectric constant which is 2000.
Also, as another technology, dielectric ceramic capacitors disclosed in JP Patent Nos. 3039417 or 3064918 are known.
In such dielectric ceramic capacitors, at least one of rare earth element oxide of Sc and Y and at least one of rare earth element oxide of Gd, Tb and Dy, are added in barium titanate. Namely, the technical art shown in JP Patent No. 3039417 aims to improve the X7R property of EIA standard and a highly accelerated lifetime of an insulation resistance by adding at least two kinds of rare earth element oxides selected from two element groups which is divided arbitrarily, to barium titanate.
However, in the technical art disclosed in JP Patent No. 3039417, since the added amount of the rare earth element is too little or so, the specific dielectric constant is 3000 or more which is large, thus the possibility that electrostriction occurring in a high electric field was high.
Further, in JP Patent No. 3064918, the dielectric ceramic composition wherein pluralities of rare earth elements are added to barium titanate is disclosed. However, in JP Patent No. 3064918, the inventive idea to divide rare earth element by large or small size of the ion radius is not disclosed.
Thus, there is a problem of the electrostriction due to a large specific dielectric constant, as similar to JP Patent No. 3039417.